READ: Electron Configurations
READ: Electron Configurations
Now that you know how electrons fill the orbitals within a sub-level, let's learn the order in which they fill different energy and different sub-levels. The way that the electrons fill the orbitals is known as the electron configuration
. Remember that the electrons determine much about the way that an atom behaves. Because they are so important, knowing the electron configuration will go a long way towards helping us understand atoms. An electron configuration shows the energy level, sublevel, and the number of electrons in that subshell.
Watch the following to learn how to write electron configurations for an element.
Noble Gas Core Configuration
After writing out the configuration for bismuth, you'll be glad to hear that there is a shortcut way to write electron configurations. This is called noble gas core configuration. As the name implies, it is based on the noble gas that is found before the element that you are writing.
Valence Electrons
The electrons that are on the outermost energy level are called valence electrons. These are not the electrons that are written last, but the ones that are in the highest energy levels. Look at the examples below and notice the energy level the valence electrons are in.
Element | Noble Gas Configuration | # of Valence Electrons |
Boron | [He] 2s 2, 2p 1 | 3 |
Iodine | [Kr] 5s 2, 4d10, 5p 5 | 7 |
Gallium | [Ar] 4s 2, 3d10, 4p 1 | 3 |
Argon | [Ne] 3s2, 3p6 | 8 |
*** A special note about the last example:If you have a noble gas, you cannot use only that element for the electron configuration. In other words, [Ar] is not the correct noble gas configuration for Argon, you have to go back to the noble gas that precedes it and move forward. Thus, the correct noble gas configuration for Argon is [Ne] 3s2, 3p6
Watch the following video on valence electrons and electron configuration theory.
Now that you can write electron configurations, you will be able to answer a question like this. Is the gaseous atom of calcium paramagnetic? Remember from the previous page that paramagnetism occurs when there are unpaired electrons in an atom. In order to answer this question, first write the electron configuration.
Now, draw the orbital diagram for the sublevel past the noble gas core electron configuration.
You can see that there aren't any unpaired electrons, so Ca is not paramagnetic.
Georgia Virtual, Atomic Theory, CC BY-NC-SA 3.0
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